That question is rarely raised today, in part because it conjures up the possibility of governments intruding into the most private and profound decision a couple can make. In a worst-case scenario, authorities could impose discriminatory policies that would limit births based on such criteria as race, ethnic origin, cultural background, religion, or gender.

But with huge, vexing questions such as food security, poverty, energy supplies, environmental degradation, and climate change facing humanity, some are asking whether aggressive measures to control population growth should be on the public agenda.

Politicians generally stay clear of suggesting population-control policies, recognizing the deep-seated concerns they raise. President Obama did not mention the issue as part of his campaign last fall. But the new Obama administration has promised to take a fresh look at solutions to energy and environmental challenges and has brought in a new slate of scientific advisers. The United States remains the only developed country without an official population policy.

Might the new administration dare to raise the idea?

“You’ve got to get a president who’s got the guts to say, ‘Patriotic Americans stop at two [children],’ ” says Paul Ehrlich, a professor of population studies at Stanford University. “That if you care about your children and grandchildren, we should have a smaller population in the future, not larger.” Professor Ehrlich wrote the groundbreaking 1968 book “The Population Bomb,” which predicted disastrous effects from unchecked population growth.